The present invention relates to a parallel processing logic circuit for sensor signal processing, which parallelly processes outputs from a plurality of sensors laid out in a rectangular grid using a plurality of processing units corresponding to the sensors.
As shown in FIG. 76A, a system that consists of a pixel array 101 in which a plurality of pixels 110 each having a sensor for detecting light or a three-dimensional pattern on an object surface are laid out in a matrix, a controller 102 for controlling the pixel array 101, and a memory 103 which stores a control program has been proposed. The system reads an image or the surface shape of an object and processes the image.
As an example of the system, a fingerprint identification system matches a fingerprint image acquired by the sensors in the pixel array 101 with a template image stored in the array in advance, thereby authenticating a person. If a deviation from an ideal pattern, such as noise or local intensity variation, is contained in the acquired fingerprint image, the accuracy of matching with the registered image degrades. To prevent this, preprocessing of removing noise or local intensity variation from the acquired image and then matching it with the template image is necessary.
This preprocessing can be executed by two methods: 1) the acquired image is temporarily read out from the pixel array 101 and sequentially processed by a general-purpose microprocessor, and 2) the image is processed in parallel by processing units 110p, each of which is integrated in a pixel 110, as shown in FIG. 76B.
In method 1), it takes a long time to read out image data from the pixel array 101 to sequentially process the data by the external microprocessor. In addition, the power consumption of the microprocessor increases when the operating frequency is raised to accelerate the processing.
To the contrary, method 2) uses parallel processing. For this reason, processing can be executed in short steps. Since the processing speed need not be increased by raising the operation frequency, unlike method 1), power consumption does not increase. In addition, since the sampled fingerprint image need not be read out from the pixel array 101, any leakage of personal information can be prevented, and the privacy is secured.
When method 2) is employed, a general-purpose microprocessor has conventionally been used as the processing unit 110p integrated in each pixel 110. This microprocessor has a logic operation block with multiple functions and a storage circuit having a sufficient capacity. So, various image processing are possible. However, it is difficult to increase the resolution of image processing since the microprocessor occupies a large area because of the high functionality. Especially, when the feature length of an image pattern such as a fingerprint is fixed, the pixel size must be equal to or less than a predetermined value (about 50 μm or less) to obtain a resolution that reflects the feature length. In the conventional scheme, the size cannot be achieved.